Projection displays for projecting an image on a screen are widely used as image display apparatuses such as television receivers and video projectors. A lamp light source is generally used in such a projection display, but the lamp light source has problems of a short life, a restricted color reproduction area and low light utilization efficiency.
In order to solve these problems, an attempt has been made to use a laser light source as a light source of an image display apparatus. The laser light source has a longer life and the light utilization efficiency thereof is more easily increased due to its strong directivity. Further, since the laser light source has monochromaticity, a color reproduction area is large and a vivid image can be displayed.
However, in a display using a laser light source (hereinafter, called a “laser display”), speckle noise produced due to high coherency of laser light becomes problematic. The speckle noise is noise of microscopic particles produced as a result of mutual interference of diffused lights when laser light is diffused on a screen and perceivable by an observer. The speckle noise is noise in which particles of the size determined by the F (F-number) of the observer's eyes and the wavelength of the laser light source are randomly arranged, disrupts the perception of an image on the screen by the observer and induces severe image deterioration.
Patent literature 1 proposes to increase the substantial aperture ratio of a two-dimensional light modulation device by using a laser light source and a microlens array and to reduce diffracted lights by increasing light utilization efficiency. However, it is not studied how to solve problems such as speckle noise in the case of using laser light.
Proposal has been made for an image display apparatus using a laser image to obtain high light utilization efficiency by utilizing characteristics of a laser light source with a small light source area and strong directivity, but no proposal has been made to achieve a balance between speckle noise removal and high light utilization efficiency by utilizing a small-size two-dimensional light modulation device.
Since the use of a laser light source as a point light source increases power density caused by beam focusing, it leads to the deterioration of light resistance of the laser light source by light focusing, which was not a problem in conventional light sources.
Patent Literature 1:
Japanese Unexamined Patent Publication No. 2002-268003